The present invention generally relates to an inflator for an air bag or cushion and more specifically to the type of inflator known as a hybrid inflator.
It is known that if the early inflation rate of an air bag is too high, the resulting deployment forces can contribute to the possible injury of an occupant who is out of the normal seated (either driver or passenger) position. If, however, the air bag inflation rate is maintained at a relatively low value, primarily to reduce such deployment forces, full deployment of the air bag may not be timely achieved.
It has for some time been appreciated that one goal of air bag inflator design is to provide an inflator which initially has a relatively low or soft inflation rate (for a relatively few milliseconds) primarily to protect the out-of-position passenger, such as a standing child, who would be subject to large deployment forces and thereafter to rapidly increase the inflation rate of the air bag to cause rapid and full inflation. The prior art shows techniques for achieving this staged (bi-level) inflation of an air bag by utilizing an inflator which is capable of producing inflation bases with at least a low and a higher rate of gas production. With regard to air bag inflators generally, whether they are of the hybrid or stored gas variety or of the solid propellant (typically sodium azide) variety is the inclusion of an initiator or squib and a mass of gas producing or propellant material. As is known in the art and in response to a crash signal, the squib (or initiator) is activated which in turn causes the propellant material to burn. In the case of a hybrid inflator the purpose of the propellant material is to heat the stored inflation gas thereby increasing the effective, released volume of same while also increasing the rate of egress of the inflation gases from a pressure tank. In this case heated, stored gas is the primary source of inflation gases. In the solid propellant type of inflator, the squib causes the propellant to burn, the purpose of which is to generate a relatively inert, large volume of inflation gases.
In order to achieve the above-mentioned staged, variable inflation rate for an inflator, the prior art has proposed using a plurality of detonating devices to sequentially open restricted and unrestricted flow paths (see U.S. Pat. No. 3,741,580). Another type of device for generating the staged inflation has been proposed in U.S. Pat. No. 3,774,807, wherein upon activation of a single detonating element a piston moves to uncover a flow passage permitting the cold egress of stored gas from a pressure tank, thereafter the piston is used to detonate a quantity of propellant which in turn heats the stored gases prior to exiting the inflator. Instead of selectively opening a flow port as described above, U.S. Pat. No. 3,948,540 shows the technique of using a spear thrower mechanism which punctures a sheer disk to permit stored gas to flow through various exit ports and inflate the air bag. Still another technique to provide the staged inflation is to use a dual electro explosive device system wherein one detonator is used to rupture a disk which initially permits the stored gas to flow into the air bag and shortly thereafter to energize the second initiator which causes the propellant to burn and as such increases the rate at which gases exit the inflator. Of the patents illustrative of inflators using two or more electro explosive elements are U.S. Pat. Nos. 3,972,545; 4,007,685; 4,136,894; and 4,358,998. Additional patents which utilize variable orifice devices are U.S. Pat. Nos. 4,006,919; 4,018,457; 4,021,058; 4,203,616; 4,268,065 and 4,619,285. Other devices utilizing sliding members or disk piercing mechanisms are: U.S. Pat. Nos. 3,910,596; 3,948,540; 3,966,226; and 4,771,914.
It is an object of the present invention to provide an inflator for providing gases to inflate an air bag having a single electrically responsive squib and one primary quantity of propellant material in order to achieve a dual or staged inflation rate of the air bag.
Accordingly the invention comprises: an inflator (110) comprising: a pressure tank for storing a quantity of stored inflation gas under pressure. The pressure tank comprising a first burst disk in communication with the stored inflation gas preventing egress of the gas from the chamber and a hollow sliding piston and including at one end thereof cutting edges for puncturing the first burst disk as the piston is thrust forward. A shear disk having a stationary outer portion and a detachable central or inner portion. The central portion is secured to one end of the piston opposite the first means. The central portion separates from the outer portion and moves with the piston. The central portion also functions as a second burst disk. A quantity of propellant material is provided near the second burst disk and produces gaseous combustion products when burned. The piston is propelled into the first burst disk after the central portion of the shear disk separates from the outer portion in response to the build up of pressure generated due to the burning of a propellant. The puncturing of the first burst disk permits the egress of the stored inflation gas. The central Portion or second burst disk which is still attached to the piston is ruptured by the continued build up of pressure due to the burning propellant material whereupon after the rupturing of the second burst disk the heated products of combustion resulting from the burning propellant material flow through the sliding piston to increase the temperature of the stored inflation gas prior to its exit from the inflator.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.